1. Field of the Invention
The present invention relates generally to endoscopic instrumentation, and, more particularly, to a disposable rigid arthroscope having a direction of view offset relative to the longitudinal axis of the arthroscope.
2. Description of the Prior Art
Endoscopes have long been used in surgery to view internal portions of a patient's body through a narrow incision in the body exterior or through a naturally occurring hollow viscus. Endoscopes are long, slender instruments having a shaft which is either rigid or flexible, depending upon the procedure being performed. In general, endoscopes include an objective lens positioned adjacent a distal end, and an image transmission system which may include a fiber optic bundle, relay rods or lenses, or a solid state sensor to transmit the image to the viewer. Endoscopes also are usually equipped with an illumination system, such as a fiber optic bundle, which illuminates the area being imaged. Generally, a camera adapter is provided at the proximal end of the endoscope to permit the image to be displayed on a monitor for viewing by the entire surgical team.
Most endoscopes used for medical procedures have a fixed forward viewing angle. Different areas of the body can be imaged by changing the position of the endoscope or, in the case of flexible endoscopes, by bending the distal tip. In these endoscopes, the objective lens is disposed perpendicular to the optical axis of the instrument such that the area directly in front of the instrument is viewed by the user.
Some endoscopes have a direction of view which is offset relative to the optical axis. Examples of endoscopes of this type are disclosed in U.S. Pat. Nos. 4,576,147 to Hashiguchi, 4,615,333 to Taguchi, 4,850,342 to Hashiguchi et al. and 5,184,602 to Anapliotis et al. Such endoscopes, sometimes referred to as inclined angle of view endoscopes, side viewing endoscopes or oblique angle of view endoscopes, make it possible to thoroughly examine interior body spaces, such as the lining of a body cavity, e.g., esophagus, intestinal walls and articular joint spaces, by rotating the instrument. Typically, these side viewing endoscopes incorporate an angle directing prism as part of its objective assembly to redirect the field of view relative to the optical axis. In accordance with the side viewing endoscope, the illuminating fiber optic bundle is typically orientated or bent at an appropriate angle at its light emitting distal end to direct light onto the field of view.
One type of endoscope which may incorporate inclined angle of view capability is an arthroscope. Arthroscopes are used to examine the interior structure of a body joint, for example, a knee, in order to determine the extent of damage to the joint. Arthroscopes are typically smaller in diameter than other types of endoscopes, such as laparoscopes, to enable the scope to fit into the relatively small joints of the bone, particularly the wrist and foot. Examples of arthroscopes are disclosed in U.S. Pat. Nos. 4,838,247 to Forkner, 5,188,093 to Lafferty et al. and 5,190,028 to Lafferty et al.
Known endoscopes and arthroscopes having an inclined direction of view such as the scopes disclosed in the aforementioned patents have their own particular shortcomings. For example, the construction of such endoscopes is typically costly, thereby precluding the economic feasibility that such scopes may be disposed after a single use. Furthermore, properly positioning and retaining the illuminating optical fibers in a manner such that the light emitting end portions of the fibers directly illuminate light in the perspective visual field direction often entails substantial modification to the endoscopic tube and/or the incorporation of adapters and/or attachments within the distal end of the scope.
U.S. Pat. No. 4,576,147 to Hashiguchi describes an endoscope with an inclined angle of view wherein a tip member, positioned within each of a lens carrying inner tube and an outer tube, and a saddle shaped pressing member, soldered to the tip member of the inner tube, cooperate to orientate the optical fiber end portions in the visual field direction. A disadvantage of the Hashiguchi '147 endoscope is that the additional components e.g., the tip members within each of the inner and outer tubes and the pressing member, need to be precisely manufactured in order to be incorporated within the endoscope, thus increasing the cost of the endoscope. Furthermore, such components require additional steps in the assembly of the Hashiguchi '747 endoscope, further increasing the cost of manufacture of the scope.
A further disadvantage with the construction of known endoscopes of the type having inclined angles of view concerns mounting the distal optical components within the distal end of the endoscope. For example, the endoscope described in U.S. Pat. No. 4,850,342 to Hashiguchi et al. incorporates several frame members which are fitted within the lens carrying inner tube to mount the objective prism and the objective lens components within the tube. The distal most cover glass of the Hashiguchi '342 endoscope is mounted via a housing member and a separate fastening ring which is fitted within an opening in the housing member.
Accordingly, it would be desirous to provide a disposable endoscope, particularly an arthroscope, having an inclined angle of view that can be manufactured and assembled efficiently. It would be further desirous for such arthroscope to direct illuminating light in the field of view without requiring extensive modification to the endoscopic tube member or the incorporation of high precision fitting members and adapters. It would also be advantageous for the arthroscope to incorporate features to positively mount the objective lens elements within the distal end of the scope without requiring additional lens mounting components.